Most master cylinders have a "bleed port" which is uncovered when the MC piston is fully retracted. This lets the fluid in the wheel cylinders/calipers flow back into the MC when the pedal is released.
If the pedal linkage is adjusted so that the MC can not travel back to it's fully released position, the bleed port will not be uncovered. This would apply to a boosted or unboosted MC.
If it was only one or two of the wheels not releasing, there are many tales of the rubber inner liner on a hose collapsing & forming a one way valve which will not let the attached cylinder release.
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